System for placing factory prefabricated housing units

ABSTRACT

A self transportable system and method for placing full size, interiorly finished factory constructed housing units the system having as basic components, a vehicular rotary crane, a snubbing frame mountable on the crane to swing with the boom thereof, a load spreader to be handled by the crane during house placement operations and a transporter to position a housing unit relative to the crane and adapted to receive the spreader for site-to-site travel.

United States Patent 11 1 Gottlieb et a1. 4

154] SYSTEM FOR PLACING FACTORY PREFABRICATED HOUSING UNITS [75] Inventors: C. Robert Gottlieb, Mobile, Ala.;

Eugene C. Lewis, Scotch Plains, NJ.

[73] Assignee: Diamonhead Corporation,

Mountainside, NJ.

[22] Filed: Jan. 22, 1974 121 App]. No.2 435,458

Related US. Application Data [62] Division of Ser. No. 312,575, Dec. 6, 1972, Pat. No.

[52] US. Cl 294/81 SF, 294/67 DB, 212/44 [51] Int. Cl. B66c 1/28 [58] Field of Search 294/67 R, 67 B, 67 BC,

294/67 D, 67 DA, 67 DB, 81 R, 81 SF;

[56] References Cited UNITED STATES PATENTS 2,646,305 7/1953 Sonderstrup 294/67 D 1 1 Jan. 7, 11975 1/1960 Sheehan 294/81 SF 2,920,917 g 3,086,661 4/1963 De $11151 294/67 DB x 3,161,309 12/1964 Baudhuin et 111. 294/67 BC x 3,258,135 6/1966 Bigge et a1. 214/394 X 3,602,375 8/1971 Martinsod... 212/14 1 ,27,905 1/1974 Whiteman 1. 294/67 DB x Primary ExaminerEvon C. Blunk Assistant Examiner-Johnny D. Cherry Attorney, Agent, or FirmLane, Aitken, Dunner 81'. Ziems 1571 ABSTRACT A self transportable system and method for placing full size, interiorly finished factory constructed housing units the system having as basic components, a vehicular rotary'crane, a snubbing frame mountable on ,the crane to swing with the boom thereof, a load spreader to be handled by the crane during house placement operations and a transporter to position a housing unit relative to the crane and adapted to receive the spreader for site-to-s'ite travel.

8 Claims, 19 Drawing Figures iuhv PATENTED JAN 7 I975 sum 02 0F 15 PATENTEBJAN 7 ms SHEET USUF 15 mEr-mm- W5 3; 858 .928

SHEET IOUF 15 FATENTEDJM 785 saw no; 15

PMENTED 71975 SHEEI IBM 15 PATEH EB 3,858,928 sum 13a? 15 PATENTEU JAN 71975 SHEU 1'4 0F 15 PATENTEU' 1 75 sum is ur 15 CROSS-REFERENCE TO RELATED APPLICATION This is a division of application Ser. No. 312,575 filed Dec. 6, 1972, now US. Pat. No. 3,831,770.

BACKGROUND OF THE INVENTION This invention relates to' systems for placing factory prefabricated housing units on individual lot site foundations and more particularly, it concerns a novel method and apparatus providing a capability for positive and precise handling of the relatively large, heavy and delicate load represented by such housing units as well as for self transportability of equipment components of the apparatus between a plurality of individual lot sites in a land project under development.

In a co-pending application Ser. No. 163,935, filed July 19, 1971 by Eugene C. Lewis, C. Robert Gottlieb and Robert M. Macy-and assigned to the assignee of the present invention, there is disclosed a method and apparatus for transporting prefabricated housing units from a factory in which the units are constructed to a remotely located land development project on which the units are to be placed permanently. In essence, the disclosed system contemplates factory prefabrication of mechanically operable, interiorly finished housing units usingtraditional building materials and structures, followed by the transfer of the units to a marine vessel such as a-barge for transportation by water to a project terminal at the land project under development. At the project terminal, the units are transferred.

to pairs of elevated storage rails from which they may be picked up by a land vehicle or transporter having a load bed capable of being positioned under the units on the elevated storage rails and raised to lift each unit lack of inherent structural integrity and corresponding need for a continuous foundation-like support at all times in transit, a load lifting or handling spreader would be needed for the final transfer and placement operation. Although the spreader structures employed in transferring the housing units to the barge provided a solution to the achievement of adequate strength to supply structural integrity to the housing unit, the combined weight of such a spreader and the housing unit could not be handled effectively by the rotary crane. Also and because of its required overall size, transportability of the spreader itself from lot site to lot site on the project under development had to be accounted for. Perhaps the most critical problem posed by the final transfer and placement operation was the handling of a load spreader both during movement into a load engaging position with respect to the housing and during movement of the loaded spreader to a position by which the house would be set on the foundation. For

example, it was found that although it was technically possible to position a housing unit on a lot foundation using tag lines and the like, the lack of positive control from the rails for subsequent land travel to the iridividvary considerably in both size and design but to facilitate handling and transporting operations, a common width or joist span is employed in all units. To optimize versatility in interior floor plan design, a common width of 30 feet has been selected and units as long as v68 feet have been built and transported using the system without damage even though the units have included completely finished and painted dry wall interiors as well as operating fixtures such as ranges, refrigerators, dishwashers, lamp fixtures and the like.

Although the system disclosed in the aforementioned co-pending application has proven in practice to be highly effective in the handling and transporting such housing units from the factory to the particular lot on which a foundation has been erected to receive the housing unit, several problems were encountered in the transfer of a unit from the vehicular transporter to its final or ultimate position on the lot site foundation. For example, a mobile rotary crane was found to be the most versatile lifting and transfer mechanism to be used at individual lot sites, taking into account such factors as capability for operating in minimal areas of low overhead clearance due to trees, utility lines for example, lifting capacity, transportability, direct commercial availability and the like. Also it has been appreciated that because of the structural characteristics of the housing unit to be lifted and transferred, specifically its over the crane suspended load made it exceedingly difficult to achieve placement of the house on the foundation with adequate precision. The slightest of breezes, for example, were found to have'a critical adverse effect on achieving and retaining a proper horizontal orientation of the unit with respect to the foundation for a long enough period of time so that it could be lowered gently onto the foundation.

The overall scheme of factory prefabrication of full size mechanically operable, interiorly finished housing units constructed with traditional building materials and transportation thereof largely by water from the location of the factory to the building project, all as disclosed in the aforementioned co-pending application Ser. No; 163,935, has therefore been found in practice to be a highly efficient and economically' sound solution to the major problems of the housing industry. A need has been demonstrated, however, for improved techniques and equipment for the final positioning of such units on a'foundation located at the ultimate individual'lot sites.

SUMMARY OF THE PRESENT INVENTION including novel procedures and apparatus is provided by which interiorly finished housing units have single floor areasas large as 30 by 68 feet and weighing as much as 67,000 pounds'are effectively transferred from a vehicular transporter to a foundation or stacked on top of another such housing unit located at the individual lot sites of a land development project. The aforementioned problems encountered as a result of actual practice have been substantially overcome by an integrated system in which the position of the housing unit suspended from the hoist line of a conventional rotary crane is positively controlled with facility for adjustment so that the unit may be located within extremely close tolerances in a highly efficient manner. In a more specific sense, the system includes a novel load spreader capable not only of providing structural integrity to the housing unit during transfer but which is of minimal weight and capable of being readily transported both from lot site to lot site and also over land as a result of ease of disassembly. The positive control over the load represented by the housing units engaged boom is effected by an unique snubbing frame arrangement which adjusta'bly anchors the load spreader and the housing unit in a horizontal reference plane with respect to the crane supported during transfer in conventional fashion on outrigger beams and jacks. In addition, the invention contemplates an unique method involving both the precise location of the component pieces of equipment to effect the ultimate transfer as well as the operation of those components during the transfer.

Among the objects of the present invention are there fore: the provision of a highly effective, integrated and self transportable systemfor placing full size, interiorly finished, factory prefabricated housing units onindividual lot site foundations; the provision of such a system by which precise positive control of housing unit positions can be maintained throughout the complete transfer operation; the provision of an unique load spreader possessing both adequate strength to supply needed structural integrity to the housing unit during transfer as well as-minimal weight and operating capabilitiesfor effective handling during operation; the provision of an unique snubbing frame arrangement'by which movement of the load spreader is precisely and accurately controlled during all phases of the operation; the provision of such a snubbing frame arrangement capable of positive adjustability thereby enabling a precise positioning of the housing unit with respect-to a foundation; the provision of such a system capable of both place ment of such housing units directly on foundationsand also for stacking such housing units to provide multistory buildingstructures; the provision of such a system which is self transportable in a highly efficient manner; the provision ofan unique method for precisely positioning the individual crane and transporter components of the system in relation to a lot site foundation; and the provision of a novel method for operating-the components ofthe system to maximize efficiency of the transfer operation as well as facilitate movement of the system component from lot site to lot site.

Other objects and further scope of applicability of the present invention will become apparent to those skilled in theart from the detailed description of a preferred embodiment to follow and taken in conjunction with the accompanying drawings in which like parts are designated by the same reference numeral.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view'illustrating the general arrangement of system components of the present invention on a lot site and relative to a foundation to which a housing unit is to be transferred;

FIG. 2 is an enlarged fragmentary cross-section of the lot site and components illustrated in FIG. 1;

FIG. 3 is a cross-section similar to FIG. 2 but illustrating in more detail the structural organization of the sys- 4. FIG. 6 is an enlarged-fragmentary cross-section taken on line 6-6 of FIG. 3;

FIG. 7 is a fragmentary cross-section taken on line 77 of FIG. 6;

FIG. 8 is an enlarged fragmentary front elevation of the lower portion of the snubbing frame as seen generally on line 88'of FIG. 5;

FIG. 9 is an enlarged fragmentary end elevation illustrating in more detail, crane mounting parts of. the snubbing frame, the overall assembly of these parts being shown in FIG. 3; v

FIG. 10 is a fragmentary plan view in partial crosssection on line I0-l0of FIG. 9 and further illustrating the crane mounting parts of the snubbing frame;

FIG. 11 is an exploded perspective view illustrating the structural parts of the loadspreader component of this invention as well as the general mode for connecting such parts;

FIG. 12 is an enlargedv fragmentary end elevation of the load spreader of the invention with phantom line illustrations of alternate positions to which it may be adjusted for movement on the house transferring vehicle or transporter component of the invention;

FIG. 13 is an enlarged fragmentary cross-section taken on line l313 of FIG. 12;

FIG. 14 is an enlarged fragmentary cross-section taken on line 14-14 ofFIG. l3;

FIG. 15 is an enlarged fragmentary cross-section taken on line 15-15 of FIG. 13;

FIG. 16 is a plan view of-the load carrying bed on the transporter component of the invention with a phantom line illustration of the load spreader in position to lift and transfer a house therefrom;

FIG. 17 is an enlarged fragmentary cross-section taken on line 1717 of FIG. 16; v

FIG. 18 is an enlarged side elevation in partial crosssection illustrating one of four spreader positioning devices mounted on the transporter component of the invention; and I FIG. 19 is an enlarged fragmentary cross-section taken on line 19-l9 of FIG. 18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT To facilitate an initial overall understanding of the system of the present invention, the components of equipment used in the system, as well as the method of house placement effected by the system, reference isfirst made to FIG. 3 of the drawings wherein a rotary or swinging boom vehicular c'rane generally designated by the reference numeral 10, is-situated in operative relation to a permanent lot foundation 12 on which a housing unit 14 carried by a semitrailer-like vehicle or transporter 16 isto be placed. The crane, in itself, is a conventional, commercially available, heavy duty,

truck crane to the extent that it includes a vehicular chassis 18 provided with usual outrigger beams 20 and stabilizing jacks 22, a cab 24 adapted to swing or rotate about a vertical axis 26 on a turntable 28 and having a boom 30 and hoisting line 32, the weight of the boom and load carried by the line 32 being balanced with a counterweight 34. In accordance with the present invention, however, the crane 10 is equipped with a novel snubbing frame 36 which is connected by way of a vertical slide and adjustable linkage assembly 38 to one side of a load spreader designated generally by the refthe present to note that the transporter generally in-- cludes a load carrying bed 42 supported at its rear end by a pair of multi-wheel trucks 44 each carrying a fifthwheel bearing plate 46 adapted for vertical adjustability with respect to the truck chassis48 by virtue ofa hydraulic jacking system (not shown). The forward end of the bed 42 is carried by a fifth-wheel tractor (not shown) also having a provision for vertical adjustability thereby completing a vertically adjustable three-point suspension by which the bed 42 may be raised, lowered or leveled. The latter of these operations is possible because each of the three points of suspension is verti' cally adjustable independent of the others.

At this point it will be apparent thatwith the house 14 located in the position illustrated in FIG. 3, and the crane l0 and spreader 40 in the positions illustrated in this figure, the house 14 may be transferred to the foundation 12 by first lifting the spreader 40 and house 14 upwardly off of the bed 42 of the transporter l6, swinging the boom 30 and spreader 40 from the solid-line position shown to a position over the foundation 12 as shown in phantom linesin FIG. 3, and the housing unit 14 lowered onto the foundation 14. While this operation would appear reasonably basic in terms of rotary crane operation, several very important factors must be accounted for to complete the operation in practice. In the first place, it will be borne in mind that the'housing unit 14 to be handled may be mechanically operable single story housing unit weighing as much as 67,000. lbs. and having dimensions as large as 30 feet in width and 68'feet in length. Moreover, the unit 14 preferably is completed finished'interiorly with plaster or plasterboard walls and may incorporate a full complement of delicate equipment including lighting fixtures, thereby establishing a load not only of substantial weightand size, but also one which is extremely delicate. Moreover, to meet building code requirements applicable to conventional houses, the unit 14 must be placed on the foundation 12 within extremely close tolerances; e.g., within 6. inch or less. It will be noted also that the slide and linkage assembly 38 effects a connection of the spreader 40 and the crane so that the housing unit 14 is at all times during its swinging movement from the transporter 16 to the foundation l4 positively or rigidly held in a generally preestablished horizontal orientation with respect to the crane 10. This positive or rigid connection between the load represented by the housing 14 and the crane 10 is essential to avoid any possibility of the housing swinging freely and erratically as a result of even the lightest winds or breezes, for example. While the linkage assembly 38 facilitates a measure of adjustability as will be apparent from the' description to follow below, the connection thereof with the crane by the snubbing frame 36 establishesa relatively fixed swinging radius of the crane, thus requiring the crane l0 and also the transporter 16 to be accurately positioned with respect to the foundation 12.

The manner in which the crane l0 and transporter 16 are positioned accurately with respect to the foundation 12 in accordance with the present invention may be understood by reference to FIGS. 1 and 2 of the drawings. In this respect, it will be appreciated that the foundationl2 will be permanently'constructed on a lot most likely to form a part of a land subdivision to be developed by using the system of the present invention as well as that of the aforementioned copending application Ser. No. l63,935. In accordance with customary practice, the lot on which the foundation is constructed is l laid out using conventional surveying techniques both to establish the'boundary lines of the lot and the precise location on each lot of the foundation 12. In addition, earth grading operations are carried out'in conjunction with the construction of the foundation. In accordance with the present invention, however, and be cause of the system thereof contemplates the transport of a substantially complete housing unit to each lot site with the aforementioned transfer of the housing unit to the constructed foundation, provision is made in the planning and construction of the foundation for the specific operative location of both the cranelO and the transporter 16 as well as the route of access to-that location in each instance. Hence, when the lot is graded to receive the foundation 12, it is graded also as necessary to provide a transporter approach roadway and a crane approach roadway 52. Although these roadways are of a temporary nature, :it has been found in practice that-they should meet certain basic requirements to accommodate the components of the system. For example, the roadway 50 should provide a firm surface for the transporter tires using temporary steel mats as necessary to insure support of the loaded transporter. Also, the transverse slope 53 of the roadway should not exceed the limits of transport bed adjustability with respect to the wheels thereof in order that the bed 42 of the transporter can be adjusted to a truly level position.

Inasmuch as the crane roadway 52 need only accommodate the unloaded crane 10, the roadway 52 itself need not be made to meet any particular specifications other than those needed to enable movement of the un loaded crane. In this instance, however, inside and outside mats 54 and56 are placed in a proper relation with respect to the foundation in advance of the time the crane It) is brought into position. The mats 54 and 56 arepositioned to underlie the pedestal jacks 22 on the crane thereby to provide a firm foundation for the crane 10 on the outrigger beams 20 during the transfer operation.

An illustrative example of the relative horizontal location of the crane 10 and transporter 16 with respect to the foundation 12 is shown in FIGS. 1 and 2 of the location and placement of the foundation 12 within preestablished dimensional tolerances to receive a par ticular housing unit 14 and meet existing building code requirements. Specifically the personnel who locate and place the foundation within such tolerances also place three aligned crane location hubs-57, 58 and 59 taking care to meet the same relatively close tolerances as those applicable to the foundation. The line on which the hubs are located in parallel with the longitudinal center line 60 of the foundation l2 and is spaced from the center line 60 by a distance the same as the radial distance R between the hoist line or cable 32 and the swing axis 26. The radial vdistance R is selected by proper adjustment of the boom 30 in a vertical plane 61 including the swing axis 26 to be optimum for the crane l'to lift the unit 14. In a more direct sense, the optimum radial distance R is predetermined by the geometry of the snubbing frame 36 and load spreader 40 though some measure of boom adjustment is contemplated to locate the cable 32 in line with the center of gravity of the unit 14 while the spreader 40 is centered on the geometric center of the unit. It will be noted that the geometric center 62 of the foundation 12and correspondingly the geometric center of the housing unit 14 are likely to be offset horizontally from the center of gravity of the unit. Inasmuch as the housing units are factory prefabricated according to plan specifications, the center of gravity may be calculated for each particular housing unit 14 to establish, for'example, a distance e equal to the longitudinal distance between the longitudinal center of the unit and the center of gravity thereof. To, correlate the location of unit center of gravity and the lifting plane of the boom 30, the center hub 58 islocated at a point offset from the transverse axis 63 of the foundation by the distance 2. Prior to moving the crane into position, the approach line of the crane is established by tying a string between the hubs 57-59 to a fourth hub 64. A plum chain 65 (FIG. 2) suspended on the swing axis of the crane will enable crane operating personnel to position the crane with reasonable accuracy over the hub 58. Having located the crane in this.manner,.the crane personnel may then locate additional hubs 68, 66 and 70 to establish the transporter approach center line 50 as well as the ultimate position thereof which'is optimum for the transfer operation. The location of the hub 68 may be determined simply by measuring the distance R from the hub 58 and selecting an optimum point on the arc defined by the radius. The hubs 66 and 70 are then set at a right angle to the plane 61. The transporter l6 and housing unit may then driven along the line 50 using plum chain 74 until the appropriate location isreached.

It might be noted that in the preceding discussion, the offset distance e applies only to the longitudinal distance between the center of gravity and the geometric center of the housing unit 14. Obviously the center of gravity may also be displaced transversely'of the geometric center'of the unit. Since this latter offset involves merely an adjustment of the angle of the boom 30 to change the radial distance R, it is not a factor in locating the crane along'the line 52.

A more complete understanding of the snubbing frame 36 and slide and linkage assembly 38 may be had by reference to FIGS. 3-9 of the drawings. As shown most clearly in FIGS. 4, 7, 8 and 10, the snubbing frame 36 includes a pair of vertical guide posts 76 and 78 each having in addition to a main intermediate section 79, upper and lower'guide post extensions 80 and 82,

respectively. The structure of both guide posts 76 and 78 as well as the upper and lower extensions 80 and 82 g is the same throughout the total length of the posts and is illustrated in FIG. 7 to include a tubular column 84 of rectangular cross-section and a laterally projecting guide flange or plate 86 welded or otherwise suitably secured to the front face of each column 84.

The guide posts 76 and 78 are secured rigidly to each other near the lower end of the intermediate or main section 79 by a beam 88 illustrated most clearly in FIGS. 4, 8 and 10 of the drawings to include a pair of end sections 90 welded in cantilever fashion to the tubular column of each guide post andconnected rigidly by bolted flange joints 92 to an intermediate beam section 94. To enable the boom 30 of the crane 10 to be lowered into a horizontal travelling position without interference by the snubbing frame 36, the beam 88 near the lower end of the guide posts 76 and 78 constitutes the sole direct interconnection of the guide posts thereby to define with the guide posts a generally U-.

shaped subassembly as may be seen in FIG. 4, for example. To provide necessary strength-against bending or deflection of the relatively long vertical lever arm represented by the guide posts 76 and 78 about the ends of the beam 88, a pair of diagonal column struts 96 extend from bolted flange connections 98 on the top of the beam section 94 upwardly and outwardly to pin and weld connections (not shown) with the posts 76 and 78 near the upper portion of the intermediate or main sections 79. Additional tube struts 100 may extend between the column struts 96 to the guide posts 76 and 78, as. shown in FIG.'8 of the drawings to lend structural integrity to the posts 76, 78 and the struts 96 as units such as-when the snubbing frame is disassembled.

The guide post subassembly thus defined by the guide posts 76, 78, the beam 88 and struts 96 is supported from the rotatable cab 24 of the crane 10 by a system of struts illustrated most clearly in FIGS. 3, 9 and 10 of the drawings. Thus, a pair of struts 102 extend from clevis pin connections 104 with gusset plates 106 welded or otherwise secured to the rear of the guide posts 76,78 near the upper end of the intermediate or main sections 79, rearwardly to clevis-pins 108 for connection to opposite ends of a beam 110 secured by brackets 111 to the top of the counterweight 34 on the crane cab 24. Compression struts 112 extend in similar fashion between the gusset plates 106 and a bracket 114 bolted or-otherwise suitably fixed to the front and of the cab 24 near the base of the boom 30. To restrain pivotal movement of the posts 76 and 78 about a point represented by the gusset plates 106, a pair of compression-tension struts 116 extend from the bracket 114 to gusset plates 117 located near the lower end of the intermediate section of the guide posts 76. As shown in FIGS. 8 and 10, a pair of diagonal struts 118 extend from a plate 119 at the center and front of the bracket 114 to pins 120 on the top of the beam and section 90 to insure lateral rigidity'in the connection of the guide posts 76 and 78 to the crane cab' 24.

Although the function of the upper and lower extensions 80 and 82 of the guides posts 76 and 78 is obviously to extend the range of vertical distance through which the guide posts are operative, it is important to the overall efficiency of the system of this invention that these extensions be easily retractable to an out-ofthe-way position. For example, the upper guide post extensions 80 would, if not retractable in this manner, inhibit translating movement of the crane 10 from lot to lot in the'project being developed particularly where overhead obstructions such as trees, utility wires and the like are present. Thus, as shown in FIG. 9, each of the upper extensions 80 has secured to its lower end a pair of plates 121 pivotally connected by pin 122 to a rearwardly projecting lug 124 secured at the upper end of the main section 79 of each of the guide posts 76 and 78. The plates 120 are provided with an additional hole [126 such that when the extension 80 and plates 120 are pivoted through 90 to an upright position illustrated in phantom lines in FIG. 9, the hole 126 registers with a 

1. A portable load spreader adapted to be suspended on a hoist line for handling large, delicate loads such as interiorly finished housing units, said spreader comprising: a detachable assembly of box-truss components including a pair of transversely spaced longitudinal struts, a pair of longitudinally spaced transverse struts, each of said transverse and longitudinal struts including interconnected spaced upper and lower pairs of tension-compression chords, detachable means rigidly interconnecting opposite ends of said longitudinal struts to said transverse struts to establish a generally rectangular superstructure, a pair of arm members also having interconnected spaced pairs of tension-compression chords, means pivotally suspending a pair of said arm members from each side of said superstructure, one from each end of said transverse struts, said pivotal suspending means detachably connecting one pair of said chords in said arm members to one pair of said chords in said transverse struts, thereby to restrict pivotal movement of said arms to a single pivotal axis and a pair of parallel truss members detachably but rigidly suspended one from each of said pair of arm members; linear load engaging and supporting means extending inwardly from each of said truss members continuously along the length thereof; and means connected between said arms and said superstructure for swinging said arms and said truss members toward and away from each other while maintaining the parallel relation of truss members.
 2. The apparatus recited in claim 1 wherein said arm members are of inverted L-shaped configuration to establish in each arm member, generally horizontal and vertical leg portions, said horizontal portion being pivotally connected at an inwardly projecting end point to the ends of said transverse struts and being of a length such that the vertical plane of said linear load engaging and supporting means in a load engaging position lies outwardly of said end point.
 3. The apparatus recited in claim 2 wherein the box-truss construction of said horizontal arm leg defines upper and lower pairs of chord members, and wherein said means for swinging said arms comprises extensible jack means associated with each of said arms connected between and operative in line with the other pair of said chord members in said transverse struts and said horizontal arm leg, respectively.
 4. The apparatus recited in claim 3 wherein said arm leg end point pivotal connection and said jack means are aligned respectively with said upper and lower pairs of chord members.
 5. The apparatus recited in claim 3 including inner and outer pivot pins connecting the inner and outer ends of said jack means to said transverse struts and said arm legs respectively, and including a common drive shaft for operating said jack means associated with each pair of arms on opposite sides of said superstructure.
 6. The apparatus recited in claim 5 including two of said drive shafts, one supported on each of said longitudinal struts for driving rotation on an axis aligned with said inner pivot pins so that upon removal of said outer pins to disconnect said jack means from said arms, said jack means can be swung about to an out-of-the-way position about said inner pivot pins without disconnection of said drive shaft.
 7. The apparatus recited in claim 1 wherein said transverse struts each include a pair of junction sections near opposite ends thereof having means to effect a clevis pin connection to opposite ends of each of said chord members in said upper and lower pairs of chord members of said longitudinal struts.
 8. The apparatus recited in claim 7 wherein said junction sections further include grommet means for connection to a suspension cable system. 